The present invention relates to an ignition distributor in an internal combustion engine and more particularly to an ignition distributor in an internal combustion engine which can suppress electromagnetic waves radiated from the discharge between a distributing electrode and side terminal electrodes constituting the distributor.
Hereinafter such an ignition distributor will be referred to as an ignition distributor for suppressing electromagnetic waves.
Some of the typical distributors hitherto well known of this kind are illustrated in FIGS. 1 and 2 of the attached drawings. FIG. 1 shows a distributor wherein the outer peripheral surface of the distributor cap of the distributor is plated by an electrically conductive metal; FIG. 2 shows a distributor where provided around the periphery of the distributor cap is a shield plate made of an electrically conductive metal. In FIGS. 1 and 2, which are side elevational views of the distributor as a whole, partially broken away, the reference numerals 1 and 2 denote a distributing electrode and a side terminal electrode, respectively, confronting each other with a gap g being left therebetween, distributing electrode 1 being adapted to be in contact with a center piece 3 to be supplied with high voltage electricity through a primary high-tension cable 4 from an induction coil, and center piece 3 is strongly urged by a spring 6 against distributing electrode 1 which is adapted to be rotated by a rotary shaft 5 that is in turn adapted to be connected to the crankshaft of the engine. Reference numeral 7 denotes a distributor cap which fixedly secures a number of circumferentially spaced side terminal electrodes 2, center piece 3 and spring 6 in position, and functions also to lead primary high-tension cable 4 to center piece 3 and secondary high-tension cables 8 to side terminal electrodes 2.
In FIG. 1 distributor cap 7 has its inner periphery plated with an electrically conductive metal 9. In FIG. 2 a shield plate 10 made of an electrically conductive metal is disposed around distributor cap 7.
In both conventional distributors shown in FIGS. 1 and 2, strong electromagnetic waves generated and radiated by the discharge between distributing electrode 1 and side terminal electrodes 2 are intended to be suppressed by an electromagnetic shield body provided on the inner surface of or around distributor cap 7. The electromagnetic shield body referred to here corresponds to an electrically conductive metallic layer 9 plated on the inner surface of distributor cap 7 in FIG. 1 or a shield plate 10 made of an electrically conductive metal arranged around distributor cap 7 in FIG. 2.
However, it has been proven that although in these conventional distributors the electromagnetic shield body is arranged around the distributor cap for the purpose of suppression of electromagnetic waves, the electromagnetic shield body cannot completely suppress the electromagnetic waves, its effectiveness therefore being not fully satisfactory.